In order to shield electronic components on a PCB in electronic devices against Electromagnetic Interference (EMI) or Radio Frequency Interference (RFI), shielding in the form of an electrically conductive shield can or box is commonly placed on the PCB so as to cover the electronic components to be shielded. EMI or RFI can be caused by external influences, or by other parts of the electronic circuit itself, such as antennas or power supplies.
Shielding can be achieved when a closed metal can with a free rim at downwardly extending side pieces is soldered to the PCB along the entire free edge of the metal can. A critical requirement that must be fulfilled in order to achieve good shielding is that the connection between the shield can free edges and the PCB is well controlled. If any areas of the free edges are not in contact with the PCB creating an electrical contact, the shielding efficiency is influenced by the largest gap between the shield can and the PCB. Therefore, if gaps exist between the shield can and the PCB, the sizes of these must be well defined. A disadvantage of directly soldering the shield can to the PCB is in the difficulty of removing the shield can once it has been attached. Some arrangements include a soldered cage around the PCB, with a removable cap to make up the shield can. This arrangement provides the permanent fixture of the shield can, whilst permitting access to the PCB; however the permitted access is limited by the soldered cage.
Soldering is not the only method of mounting a shield can to a PCB; other methods include the use of shield clips fixed to the PCB, an example of which is shown in FIG. 1. The shield clips “pinch” the free edges of the shield can, the shield clips applying a force to two opposite faces of a free edge of the shield can in order to retain its position. Using shield clips provides the advantage of removably securing the shield can to the PCB. A disadvantage of such methods is that the permitted thickness of the shield can is limited by the size of the shield clips. Also, since the shield can typically sits on top of the base of the shield clip, and not flush with the PCB itself, gaps will exist between the shield can and the PCB, reducing the Electromagnetic Compatibility (EMC) performance of the shield can. The use of shield clips can also increase the space required to fit the shield can on the PCB. In today's world, there is a constant need to reduce the size of electronic circuits, including PCBs; any arrangement that reduces the space requirements for a shield can on a PCB is highly desirable.
There also remains a need to provide removable retention of a PCB shield can, whilst maintaining EMC performance.